1. Field of the Invention
This invention relates to ultrafine particles and their production process and use. In particular, it relates to ultrafine particles capable of functioning effectively as an anti-reflection film in a cathode ray tube, a process for the production thereof and use thereof.
2. Related Art
A technique of mixing two types of ultrafine particles having different functions and using the mixture for a specific purpose has hitherto been known. In this case, it is required to meet two different functions simultaneously. The reality is, however, that since both of the functions are diluted, obtained products have little practical utility.
On the other hand, a cathode ray tube has required both formation of an electrically conductive film for prevention of a charge on a glass surface thereof and a device for prevention of reflection.
Meanwhile, it is known that the front panel surface (image display face plate) of a cathode ray tube such as a Braun tube, etc., takes a charge. The reason therefor is that, while a thin and uniform aluminum film 11 is deposited on a phosphor 10 applied to an inner surface 9 of a Braun tube 7 as shown in FIG. 3, if a high voltage is applied to the aluminum film 11, electrostatic induction causes a phenomenon of charge generation on a front panel 12 of the Braun tube when it is applied and cut off.
Japanese Patent Kokai (Laid-Open) No. 51101/1986 discloses a process for forming an electrically conductive anti-reflection film to prevent not only charge generation but also reflection on the surface of such a display tube. In this case, firstly, an electrically conductive film is formed on a glass substrate by a physical gas phase process or chemical gas phase process such as a vacuum deposition process, sputtering process, etc., and then an anti-reflection film is formed thereon.
As stated above, however, mixed ultrafine particles have a drawback in that the functions of the ultrafine particle materials are diluted. Meanwhile, formation of a laminate of two films of ultrafine particles has problems on producibility, costs and film strength.
In particular, the above prior art uses a technique of forming a two-layered structure in which an electrically conductive film and an anti-reflection film are formed, respectively, and it has posed problems in manufacture and costs. Further, in case of formation of a film on the surface of a display tube such as a Braun tube, etc., in which a film firing temperature is limited to a low temperature, there have been problems in film strength and reflectivity.